Inhibition of target tissue activation of N'-nitrosonornicotine and N-nitrosopyrrolidine by dietary components.

Twenty-one dietary and related chemicals have been evaluated for their potential inhibitory activities against the tumorigenic effects of N-nitrosopyrrolidine and N'-nitrosonornicotine using in-vitro metabolic assays in the target tissues, namely, rat liver microsomes and cultured rat oesophagus, respectively. Compounds studied include phenols, cinnamic acids, coumarins, isothiocyanates and indoles. Isothiocyanates were the most potent inhibitors of both nitrosamines in the acute studies, but were less active in chronic studies. This difference may be explained by the pharmacokinetic properties of these compounds. Phenols, cinnamic acids, coumarins and indoles were primarily inducers of N-nitrosopyrrolidine metabolism. The results suggest that isothiocyanates, in general, are the most promising chemicals for future study as protective agents against the carcinogenic effects of these nitrosamines.